Sección Especial: 37th AMASON / Special Section: 37th AMASON Ionosphere, Mesosphere and Lower Thermosphere
Latitudinal - seasonal model of the temperature response
of the middle atmosphere to solar activity
A. I. Semenov(1,*)
, V. Yu. Khomich(2)
1. Obukhov Institute of Atmospheric Physics, Russian Academy Sciences, Russia. 2. Institute of Electrophysics and Electric Power RAS, Russia.
Recibido / Received: 30/01/2011. Aceptado / Accepted: 30/08/2011. ABSTRACT:
Based on rocket and nightglow measurements at middle atmosphere heights covering several cycles of low solar activity, characteristics of seasonal response of mean monthly atmospheric temperature to solar activity are obtained at different heights of the atmosphere at middle and high latitudes. These results are used in the development of an empirical model. which allows the determination of the atmospheric temperature response as a function of latitude, month of the year and level of solar activity at heights of 30-90 km.
Keywords: Middle Atmosphere, Temperature Response, Solar Activity, Model.
REFERENCIAS Y ENLACES / REFERENCES AND LINKS
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A lot of attention has been paid recently to studying the response of the middle atmosphere to solar activity . In many respects this is caused by the fact that for correct estimation of the observed long-term temperature variations at different altitudes using data obtained for different periods, it is necessary to reduce these data to uniform conditions in order to eliminate the effect of solar activity. However, available models of the middle atmosphere cannot be used for this purpose since the effect of solar activity at altitudes of 30–95 km is not represented. Some estimates of the effect of solar activity on the character of vertical temperature distribution were considered in review . In this review the results of the measurements performed using the hydroxyl emission and the method of falling spheres [2,3] at high latitudes and a lidar [4,5] at midlatitudes were summarized. The authors of the review indicate that the results can not be explicitly used to understand the observed trends at different latitudes because short periods of observations used in analyses hinders reliable separation of the effects of solar activity and long-term trends. The present work studies the response of the average monthly temperatures of the middle atmosphere to solar activity based on long-term data obtained using rocket measurements  and spectrophotometry of the natural atmospheric emissions during several 11-year solar cycles at low, middle, and high latitudes . In addition to the long-term rocket measurements the results of the spectro-photometric measurement of the hydroxyl emission, obtained on Spitsbergen (81ºN ) were used to analyze the response of the average monthly temperatures of the high-latitude middle atmosphere to solar activity.
2. Results of measurements and the
The response of temperature to solar activity at midlatitudes was revealed using the vertical temperature profiles (30–110 km)  obtained from rocket measurements at altitudes of 30–80 km and spectrophotometric measurements of the hydroxyl (87 km), sodium (93 km), and atomic oxygen (97 km) emissions. The vertical temperature distributions at midlatitudes are presented in  for all months for the years of maximal (1980, F10.7=198, and 1991, F10.7=208) and minimal (1976, F10.7=73, and 1986, F10.7=75) solar activity.
It should be noted that the errors in individual rocket temperature measurements varied from ~3 K at altitudes of 20–45 km to 6 K at 65–80 km altitude. The average monthly temperature profiles were constructed using the data of not less than ten rocket launches in a month, which considerably decreased the errors of the average monthly temperature profiles (1– 2 K depending on altitude) . The error of the spectrophotometric temperature measurements was 2 K. For low, middle, and high latitudes, the average monthly vertical temperature profiles at altitudes of 20– 80 km for the considered years of maximal and minimal solar activity (Fig. 1) were constructed based on the rocket measurements at the Thumba (8.5°N), Volgograd (48°N), and Heiss Island (80.6°N) stations. The data of spectrophotometric temperature measurements for the middle and high latitudes have been taken into consideration.
Fig. 1: Vertical distributions of the average monthly temperatures in the middle atmosphere at (a) low, (b) middle, and (c) high latitudes for the years of solar activity minimums (1976, F10.7=73, and 1986, F10.7=75) and maximums (1980, F10.7=198, and 1991,
F10.7=208). The temperature profiles for each month are shifted to the right relative to the previous profile by 10 K. The first profile on the left corresponds to January.
the years of high and low solar activity, the rate of temperature rise due to solar activity can be found in the following form using a linear approximation : under the action of solar activity can be found in the following form in a linear approximation :
∆𝑇(𝑍) =𝛿𝑇𝐹(𝑍)𝐹10,7100−130𝐾, (1)
where 𝛿𝑇𝐹(𝑍) =𝑑𝑇/𝑑𝐹 is the temperature
change at altitude 𝑍 for 𝐹10,7=100 sfu. The
seasonal variations were constructed upon determining 𝛿𝑇𝐹(𝑍) for different altitude levels.
These dependences were approximated by the sum of four harmonics in order to reveal regular patterns. Thus,
𝑎𝑛 [𝑡𝑑− 𝑡𝑛(𝑍)]�,
where 𝑇𝑎𝑛=365.2425 days is the duration of a
year, and 𝑡𝑑 is one day of a year.
The vertical variations in the amplitude 𝐴𝑛(𝑍) and phase 𝑡𝑛(𝑍) were approximated using
the polynomials as functions of altitude 𝑍:
𝐴𝑛(𝑍) =� 𝑎𝑛𝑘�100𝑍 � 𝑘
𝑡𝑛(𝑍) =� 𝑏𝑛𝑘�100𝑍 � 𝑘 9
The results of the approximation 𝛿𝑇𝐹(𝑍) for
the equatorial, middle, and high latitudes are shown in Fig. 2 (solid lines); dots are the data of measurements smoothed by three-month moving averages in order to eliminate random outliers. These data represent insignificant temperature differences (~2–10 K), which are determined for different levels of solar activity between vertical profiles. It should be noted that the average temperature value for the considered altitudes was ~200 K.
The authors of  presented the 𝛿𝑇𝐹(𝑍)
ÓPTICA PURA Y APLICAD
unchanged, although it has a maximal value. Therefore, the spread in the values is apparently caused by the seasonal character of observations. Nevertheless, it should be noted that the results obtained in Wuppertal (midlatitudes)  almost coincide with the average response values at midlatitudes shown in Fig. 2. The lidar midlatitude measurements (1978–1989) at altitudes of 33–75 km  also indicated that the response changes its sign in winter and summer depending on altitude. These researchers obtained that the response values at altitudes of 60–70 km were ~5 and ~3
K/100 sfu in winter and summer, respectively. For altitudes about 40 km, these authors obtained that the values were about –6 and –1
K/100 sfu in winter and summer, respectively. In order to extend the analysis over a range of latitudes, an assumption has been made that the variability in the response of the atmospheric temperature in the Southern hemisphere is similar to that observed in the Northern hemisphere. Naturally, the difference in the seasons for Southern and Northern hemispheres was taken into account.
Fig. 2. Vertical distributions of the temperature response
𝛿𝑇𝐹(𝑍) to solar activity for different months of the year at (a)
polar, (b) middle, and (c) low latitudes. Dots are data of measurements; solid lines, approximations. For polar latitudes, the 𝛿𝑇𝐹(𝑍) values at an altitude of 87 km are
presented according to [8,15]. MA is the average annual vertical distribution.
Figure 3 shows the altitude distribution of the atmospheric temperature response to solar activity over the latitude range from 80 S up to 80 N for all months of year. Apparently, the temperature response is observed for all months of the year ranging from -10 up to +10 K/100 sfu. At heights above 55 km for the entire latitude range, the response is practically always positive, reaching the highest values in the polar and equatorial regions. Below 55 km, the response is negative during the equinoctial periods for the considered latitude range. During winter and summer the response is negative in polar and equatorial regions while at middle latitudes the response exhibits weak positive values (up to +4 K/100 sfu) in both hemispheres. Such a behavior of seasonal change of temperature response in the middle atmosphere is obviously associated with features of the altitude distributions of chemically active gas components and the influence of the solar UV radiation, in many respects defining the altitude distribution of temperature.
The obtained profiles of the temperature response of the middle atmosphere at various heights on solar activity for the equatorial, middle and polar latitudes show altitude nonlinearity.
At low latitudes, a positive reaction of a temperature regime to solar activity at heights of 50-70 km (up to +10 K/100 sfu) is observed. For the height range of 30-50 km, the temperature response is practically absent for winter period and negative for summer (-2 K/100 sfu). Above 70 km, a tendency for a negative monthly temperature response is observed.
At the middle latitude at heights of 55-70 km, the changes of the response are usually small (+2 K/100 sfu for winter and -1 K/100 sfu for equinoxes). At stratospheric heights of 30-55 km, noticeable changes exist in winter and spring (+5 K/100 sfu). The greatest seasonal variations are found at heights of 80-95 km (-5
Fig. 3. The altitude distribution of the temperature response of an atmosphere on solar activity in the latitudinal range from 80 S up to 80 N for all months of year.
The negative response of the temperature regime to solar activity at altitudes of the stratosphere and the positive response at altitudes of the mesosphere, with no insolation during the prolonged period of the polar night, are typical for high latitudes. In summer, when the polar atmosphere is sunlit around the clock for several months, the temperature behavior up to altitudes of 50 km changes insignificantly. The difference becomes pronounced above 50 km, when the positive response to solar activity is considerable (up to 10 K/100 sfu).
The presented results highlight the importance of accounting for solar activity variation impacts in the analysis of long-term
behavior of the temperature regime of the middle atmosphere at the different heights and latitudes. Without considering these effects, one can misinterpret the results of long-term temperature regime changes obtained at different stations and for the various heliogeophysical conditions.
This study was supported by Program of Presidium of the Russian Academy of Science
№16, part 3 and by the Grant of RFBR № 10